Interaction of the [GaH4]− Anion with Weak XH Acids− A Spectroscopic and Theoretical Study

The dihydrogen bonding (DHB) between the hydride atom of the [Bu₄N][GaH₄] salt and different XH acids, namely CF₃CH₂OH, FCH₂CH₂OH, iPrOH, MeOH, indole and 4‐O₂NC₆H₄NH₂, has been investigated for the first time by low‐temperature IR spectroscopy. The DHB spectroscopic and thermodynamic parameters in solvents of low polarity and high basicity (E_j = 1.37) were obtained. The nature, structures, energies and electron distributions of the model DHB complexes of GaH₄⁻ with H₂O, MeOH, CF₃OH, H₂NCF₃ or NO₂C₆H₄NH₂ were studied by DFT calculations and compared with those of the analogous complexes of BH₄⁻ with H₂O, MeOH or CF₃OH. Two types of DHB structures with monodentate and symmetric chelate coordination were found. The lengthening of the X−H and Ga−H bonds, electron polarization and overlap population of the H···H bond are greater in the first type of structure. A comparative analysis of experimental data demonstrates that the spectroscopic and thermodynamic characteristics, e.g. ν(XH) and ν(GaH) band shifts, ν(XH)_bonded integral intensities, formation enthalpies and E_j of all the DHB complexes increase down the group (BH₄⁻·HX < GaH₄⁻·HX). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)